The invention relates to a method and to an apparatus for operating an automated change-speed gearbox.
DE 198 23 764 A1 describes a method for controlling an automated clutch, which is included in the drive line of a motor vehicle, in conjunction with an automated gearbox. The automated clutch is controlled by an electronic control unit that evaluates the activation of an anti-lock control system (ABS), among other factors.
DE 36 30 750 A1 describes an apparatus for clutch actuation in conjunction with a manually actuated gearbox, in which a clutch arranged between the gearbox and a prime mover in the form of an engine or motor is opened when an anti-lock function of an anti-lock control system (ABS) is present. Once the anti-lock function has come to an end, the clutch is closed again. The selected gear in the gearbox can only be influenced by a driver of the vehicle.
Faced with the situation, it is an object of the invention to propose a method and apparatus for operating an automated change-speed gearbox which allows particularly comfortable operation of the change-speed gearbox.
According to the invention, the object is achieved by a method which is carried out by a control device, which controls actuators for actuating an automated clutch and for actuating gear-change elements. Selection of the gears can be performed by a driver of the vehicle by an operating device in a semi-automatic mode, or can be performed by the control device in a fully automatic mode. The control device communicates via signals with a control unit of an anti-lock control system. Via this signal link, the control unit sends signals on the current status of the anti-lock control system, such as whether the system is active, or sends requests to the automated change-speed gearbox, which are implemented by the control device. As a function of these signals, the control device sets the change-speed gearbox to a neutral position. In the neutral position, no gear is engaged in the change-speed gearbox; there is therefore no power-transmitting engagement between an input and an output of the change-speed gearbox.
Before a gear is engaged again and power-transmitting engagement is thus established between a prime mover and driven wheels of the motor vehicle, an appropriate gear ratio and hence a gear to be engaged is selected. Selection is made on the basis of variables that describe the state of the motor vehicle and the environment, and of actuating inputs by the driver of the vehicle, such as, for example:                speed of the motor vehicle        acceleration of the motor vehicle        angle of the accelerator pedal        rotational speed of the prime mover        uphill or downhill gradient of the roadway        straight roadway or a bend.        
The selection of the appropriate gear ratio is comparable with the selection of a gear in fully automatic operation of the change-speed gearbox.
Once the optimum gear ratio has been determined, this gear is engaged, and power-transmitting engagement is thus re-established. Before engagement, the rotational speed of the prime mover can be adjusted in such a way, by a request of the control device of the change-speed gearbox to the control device of the prime mover, that there is as small as possible a rotational-speed difference at the gear-change element of the gear to be engaged.
This method allows particularly comfortable operation of the change-speed gearbox. Thanks to the selection of the appropriate gear ratio for engagement, engagement can proceed very smoothly, and unnecessarily large jumps in the rotational speed of the prime mover can be prevented. Moreover, this ensures that engagement of the gear is not immediately followed by a further gear change. This is advantageous especially in the case of change-speed gearboxes with an interruption in tractive effort when changing gear. In addition, large jumps in torque at the driven wheels are prevented, leading to increased driving stability and hence driving safety.
As a refinement of the invention, if a closed-loop control function of the anti-lock control system is present, the change-speed gearbox is set to a neutral position. The necessary information for detection of a closed-loop control function is sent to the control device by the control unit of the anti-lock control system. Once the closed-loop control function has been completed, an appropriate gear ratio is determined and this gear ratio is engaged. It is also possible for an appropriate gear ratio to be determined continuously even during the closed-loop control function, this gear ratio then being engaged immediately on completion of the closed-loop control function.
In the case of a closed-loop control function of the anti-lock control system, a braking force at the vehicle wheels is lowered and raised during a braking operation in such a way that the wheels are prevented from locking up. During this process, vibrations may be excited in a drive line comprising driven wheels, a final drive, a drive shaft, a change-speed gearbox and a prime mover if there is power-transmitting engagement between the prime mover and the driven wheels. This refinement of the invention is particularly comfortable since no vibrations can be excited owing to the neutral position of the gearbox.
As a refinement of the invention, the change-speed gearbox is set to the neutral position after an initial request from the control unit of the anti-lock control system. When power-transmitting engagement is to be re-established, the control unit sends the anti-lock control system an appropriate second request or stops sending the first request. An appropriate gear ratio is then determined, and this gear ratio is engaged. The initial request can take place before or after the start of a closed-loop control function of the anti-lock control system, and the second request can take place before or after the end of the closed-loop control function. This means that the change-speed gearbox is operated in a particularly comfortable manner since the change-speed gearbox can be set to the neutral position even before the closed-loop control function of the anti-lock control system starts, and thus no vibrations can be excited. Moreover, it is possible for the neutral position to be requested only when this is necessary for reasons of comfort or safety.
As a refinement of the invention, before the change-speed gearbox is set to the neutral position, a clutch arranged between the prime mover and the change-speed gearbox is opened and the clutch is closed once the appropriate gear ratio has been engaged. In this case, the clutch can be designed as a single or double clutch. The power-transmitting engagement between the prime mover and the driven wheels can be interrupted in a particularly rapid and jerk-free manner through the opening of the clutch. With the clutch opened, the change-speed gearbox can be set to the neutral position in a jerk-free manner and hence in a particularly comfortable way. Moreover, this can be carried out without imposing a load on the gear-change elements, this increasing the life of the gear-change elements. The same applies mutatis mutandis to the engagement of the gear.
As a refinement of the invention, a torque that can be transmitted by the clutch is reduced as a function of variables that describe the state of the motor vehicle. The torque that can be transmitted is the torque that can be transmitted without slipping of the clutch or slip at the clutch. For example, variables that indicate potential imminent changing of the change-speed gearbox to neutral are evaluated, for example:                gradient of a brake pedal travel        gradient of a pressure in the brake system        vibrations at the wheels and/or axles of the motor vehicle.        
If one or more variables exceed certain thresholds, the clutch torque is reduced. If the change-speed gearbox is set to the neutral position in response to a request by the control unit of the anti-lock control system, the torque that can be transmitted can be reduced in the event of a closed-loop control function of the anti-lock control system.
The clutch is opened and the torque that can be transmitted therefore reduced to an extent such that the torque of the prime mover can still be reliably transmitted, for example. Thanks to the partial opening, the clutch can be completely opened more quickly if necessary. The method according to the invention thus acts more rapidly, and particularly comfortable operation of the change-speed gearbox is achieved.
As a refinement of the invention, the method is only carried out if variables that describe the state of the motor vehicle are less than certain limiting values. For example, variables that indicate dynamic operation of the motor vehicle, such as                the steering angle        the lateral acceleration of the motor vehicle        the longitudinal acceleration of the motor vehicle        and the yaw rateare evaluated. The method is carried out only if one or more variables are less than certain limiting values.        
In the case of dynamic operation of the motor vehicle, re-establishment of power-transmitting engagement between the prime mover and the driven vehicle wheels can lead to instability. Suppressing the implementation of the method in such situations allows particularly safe operation of the motor vehicle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.